Oilpan: move MediaKeyError to the heap.

Source/modules/encryptedmedia/MediaKeySession.cpp

 /*
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 280 matching lines @@
     m_isClosed = true;
 
     if (m_actionTimer.isActive())
         m_actionTimer.stop();
     m_pendingActions.clear();
     m_asyncEventQueue->close();
 }
 
 void MediaKeySession::trace(Visitor* visitor)
 {
+    visitor->trace(m_error);
     visitor->trace(m_asyncEventQueue);
     visitor->trace(m_keys);
     EventTargetWithInlineData::trace(visitor);
 }
 
 }